MORPHOLOGICAL CHARACTERISTIC AND FORMATION MECHANISM OF JOINT OF MELT-SPUN Cu-Sn ALLOY FOILS BY CAPACITOR DISCHARGE WELDING
Morphological Characteristic and Formation Mechanism of Joint of Meltspun Cu—Sn Alloy Foils By Capacitor Discharge Welding

The connection behavior and joint microstructure of capacitor discharge welding for melt--spun Cu--20%Sn alloy foils are investigated by using a micro--type capacitor discharge welding machine. The micro joint consists of nugget zone, semi--melt zone and heat affect zone. The rapid solidification microstructure characterized mainly by fine b--Cu5.6Sn equiaxed grains are produced in the nugget. The thickness of semi--melt zone is only 2.0---3.0um and there is no obvious change of microstructure in heat--affected zone. Under the electrode pressure and electromagnetic force, the liquid phase flow occurs in undercooled nugget, which is symmetrical about the electrode axis and connection interface and results in the formation of curving streamline. The porosity is the main welding defect produced during welding. With the increase of electrode pressure pm, the radius of porosity sharply decreases. If the electrode pressure is more than 1.0 MPa, this decrease tendency becomes smooth. The liquid phase flow promotes the collision, coalescence and movement of bubbles, resulting in that porosities distribute along the periphery of nugget.